In the downhole drilling and completion industry, the formation of boreholes for the purpose of production or injection of fluid is common. The boreholes are used for exploration or extraction of natural resources such as hydrocarbons, oil, gas, water, and alternatively for CO2 sequestration. To increase the production from a borehole, the production zone can be fractured to allow the formation fluids to flow more freely from the formation to the borehole. The fracturing operation includes pumping fracturing fluids including proppants at high pressure towards the formation to form and retain formation fractures.
Efforts are continually sought to improve methods for conducting multi stage fracture treatments in wells typically referred to as unconventional shale, tight gas, or coal bed methane. Three common methods currently in use for multi stage fracture treatments include plug and perf stage frac'd laterals, ball drop frac sleeve systems, and coiled tubing controlled sleeve systems. While these systems serve their purpose during certain circumstances, there are demands for increasing depths and flexibility and increasing number of stages. For example, balls and landing seats used in ball drop frac sleeve systems have a limited number of stages in cemented applications and require expensive drill out.
A conventional fracturing system passes pressurized fracturing fluid through a tubular string that extends downhole through the borehole that traverses the zones to be fractured. The string may include valves that are opened to allow for the fracturing fluid to be directed towards a targeted zone. To remotely open the valve from the surface, a ball is dropped into the string and lands on a ball seat associated with a particular valve to block fluid flow through the string and consequently build up pressure uphole of the ball which forces a sleeve downhole thus opening a port in the wall of the string. When multiple zones are involved, the ball seats are of varying sizes with a downhole most seat being the smallest and an uphole most seat being the largest, such that balls of increasing diameter are sequentially dropped into the string to sequentially open the valves from the downhole end to an uphole end. Thus, the zones of the borehole are fractured in a “bottom-up” approach by starting with fracturing a downhole-most zone and working upwards towards an uphole-most zone.
While a typical frac job is completed sequentially in the bottom-up approach, an alternating stage process has been suggested in which a first interval is stimulated at a toe, a second interval is stimulated closer to the heel, and a third interval is fractured between the first and second intervals. Such a process has been indicated to take advantage of altered stress in the rock during the third interval to connect to stress-relief fractures from the first two intervals. Fracing zones alternately or out of sequence enhances results and improves production, but existing methods are not readily adaptable to this process, and accomplishing this process is not possible with conventional equipment.
Also, conventional multi stage frac methods do not have the technology to evaluate data real time and optimize their operations appropriately. The ability to provide critical real time data to evaluate and properly conduct operations is a desirable feature in downhole operations. Existing methods for installing electrical control lines, however, require splices or connections at each device or monitoring point. These splices require excessive rig time and are prone to failure. In addition, transmission of large amounts of power through control lines is problematic.
As time, manpower requirements, and mechanical maintenance issues are all variable factors that can significantly influence the cost effectiveness and productivity of a multi-stage fracturing operation, the art would be receptive to improved and/or alternative apparatus and methods for downhole communications and improving the efficiency of multi-stage frac operations. The art would be receptive to alternative devices and methods for alternating a sequence of a frac job.